The invention pertains to a flexible cord-like hollow object with an inner zone, which is enclosed by a casing, for the transportation of media.
Flexible cord-like hollow objects of this generic type are known. These cord-like hollow objects, which are also called tube[s] below, are used in many sectors of industry for the transportation of liquid or gaseous media. Such tubes are used for the transportation of refrigerants for use in technical climate control units, e.g. in motor vehicles. Refrigerants have the property that they are volatile and lead to harmful effects when they get into the earth""s atmosphere. In order to avoid this, use should be made of natural refrigerants, e.g. CO2. In the case of known refrigerant tubes, it is a disadvantage that these are not diffusion-proof and that they exhibit high permeability to natural refrigerants, especially carbon dioxide CO2.
A flexible pipe for the transportation of media is known from EP 0 375 608 A1 in which a barrier layer is integrated into the casing of a flexible cord-like hollow object in order to reduce permeation.
The barrier layer is formed from a longitudinal or spiral-shaped metal foil that is overlapped at the edges of the strip. In the case of this arrangement, it is a disadvantage that freedom from leakage of the barrier layer cannot be ensured adequately especially in the event of a high bending stress.
Thus the objective of the invention is to create a flexible cord-like hollow object of this generic type that has low permeability in combination with high flexibility, especially in the case of CO2.
In accordance with the invention, this objective is accomplished by means of a flexible cord-like hollow object with the characterizing features that are designated in Claim 1. As a result of the feature that a barrier layer, which is impermeable to the volatile molecules of the medium that is to be transported, is integrated into the casing of the hollow object and that the barrier layer comprises sub-elements that are arranged in a scale-like manner, permeation through the flexible cord-like hollow object is prevented with high efficiency or it is at least reduced to a negligibly low value. Thus it becomes possible to transport refrigerants without the volatile components of the refrigerant being able to get into the atmosphere, especially when, as is preferred, the flexible cord-like hollow objects are used as a refrigerant tube. A low rate of permeation simultaneously ensures reliable functioning of the refrigeration unit that is to be supplied with the refrigerant. In particular, the scale-like arrangement of the sub-elements permits stressing due to bending of the flexible hollow object as previously. Because of the overlapping of the sub-elements, this freedom from leakage of the barrier layer is not impaired during stressing due to bending. The scale-like arrangement of the sub-elements leads to the situation in which the barrier layer does not break during stressing due to bending. Breakage or damage to the barrier layer would lead to an increase in the rate of permeation.
The scale-like construction can be achieved in a very advantageous manner by producing an appropriate crystal structure during the vapor deposition of the metallic barrier layer that is preferably provided.
The scale-like construction for the crystal structure can preferably be obtained via the vapor deposition of a crystalline substance on a layer of the casing that serves as a carrier layer, whereby the crystalline substance comprises e.g. metal or a synthetic material. As a result, crystalline regions (platelets) are produced, which are absolutely impermeable, on the surface of the layer of the casing that serves as the carrier. As a result, the situation is reached in the non-expanded state, i.e. the non-stressed state, that the flexible cord-like hollow object (tube) is almost completely impermeable to the refrigerant that is to be transported. Negligibly low permeation can arise only through extremely small seams between the vapor deposited platelets. If the platelets are vapor deposited in such a way that they overlap, then a degree of overlapping of the platelets can be ensured even during stressing due to bending or tensile stressing of the tube so that, for example, 99% of the total surface is covered with the crystalline platelets even in such a state of the tube.
An advantageous feature, in particular, as a result of this is that use can be made of the flexible cord-like hollow object, which has been provided with the crystalline platelets, even in the high pressure range and the low permeability remains intact. Such high pressure expansion tubes, which have been provided with such a barrier layer in accordance with the invention, excel by virtue of their high flexibility, shrinkage attenuation and favorable effect on acoustics so that these advantages can be exploited along with the simultaneous assurance of low permeability.
In particular, use can be made of carbon dioxide CO2 as the refrigerant in high pressure expansion tubes that have the barrier layer in accordance with the invention. The use of carbon dioxide as the refrigerant in the high pressure range leads, as such, to the problem of so-called decompressive explosion in the event of a sudden drop in pressure. The formation of large aggregates of the refrigerant occurs abruptly in a material that is in contact with the refrigerant. This would lead to damage or, as the case may be, the destruction of the material. As a result of the barrier layer in accordance with the invention, the situation is now reached in which damage to the material, i.e. the casing of the flexible cord-like hollow object here, cannot occur since permeation of the molecules of carbon dioxide, which is used as the refrigerant, into the casing is prevented.
Permeation is prevented or, as the case may be, reduced to a negligible minimum even in the case of high pressure expansion because of the aforementioned scale-like arrangement of the crystalline platelets in particular.
Moreover, it is preferable if the barrier layer comprises sub-elements that have been arranged in a scale-like manner, whereby the sub-elements overlap in the longitudinal extension of the hollow object and/or coaxially relative to a longitudinal axis of the hollow object. As a result, a leakage-proof arrangement of the barrier layer is achieved that, moreover, impairs the flexibility of the hollow object only to an insignificant extent.
In a preferred form of embodiment of the invention, the feature is provided that the barrier layer is arranged on the outer casing surface of an inner layer of the casing. As a result, it becomes possible and preferable to integrate the barrier layer into the casing without this [casing] impeding the cross section of the inner zone of the hollow object. The inner casing surface of the inner layer of the casing can thus be optimized in terms of the medium that is to be transported so that flow resistance, which is as low as possible, is provided. However, the barrier layer, which is applied to the outer casing surface of the inner layer, prevents the diffusion of the volatile components of the medium, which is to be transported, through the casing. In the event that these diffuse through the inner layer of the casing, they then encounter the barrier layer and they cannot pass through the casing. Thus the low permeability of the casing is ensured.
In a further preferred form of embodiment of the invention, the feature is provided that the barrier layer comprises metal or a synthetic material. As a result, a material can be selected in a simple manner that is optimal for the medium that is to be transported, whereby the material exhibits especially good barrier action with respect to the volatile components of the medium that is to be transported.
Moreover, the feature is provided in a further preferred form of embodiment of the invention that the barrier layer is connected to the outer casing surface of the inner layer of the casing in a non-positive [adherent] manner. As a result, the situation is reached in which detachment of the barrier layer can be prevented during subsequent usage of the flexible cord-like hollow object in accordance with directions so that the low permeability, which has been achieved, remains intact. The feature is preferably provided that the casing surface is treated physically and/or chemically in order to increase the strength of adhesion between the barrier layer and the casing surface. As a result, roughening can be achieved, preferably and in particular, and this ensures better adherent bonding to the subsequently applied barrier layer.
In particular, it is preferred that an increase in the strength of adhesion between the barrier layer and the casing surface be obtained via the polarization or activation of the material of the casing at least in the surface region of the casing surface of the inner layer of the casing. Depending on the material of the casing, which preferably comprises a polymer, polar groups can be incorporated, as a result, into the basic molecular structure of the casing, whereby these polar groups ensure an improvement in the coating of the casing surface with the barrier layer.
In a preferred form of embodiment of the invention, moreover, the situation is provided in which an additional bonding agent is arranged between the barrier layer and the casing surface. This additional bonding agent leads to an especially strong and durable non-positive [adherent] joint between the barrier layer and the casing so that the adherent bonding between the barrier layer and the casing remains intact even with relatively intense mechanical stressing during usage, which is in accordance with directions, and its low permeability can be maintained.
Further preferred forms of embodiment of the invention result from the remaining characterizing features that are designated in the subsidiary claims.